Studies will be designed to indicate whether a fatty acid that allows rapid and extensive cellular growth does so by its effectiveness as a biosynthetic substrate or by the effectiveness of its resultant products. These studies are designed to provide a fundamental insight into the metabolic process by which a saturated fatty acid or an unsaturated fatty acid may be perceived by living cells. The successful extension of selective quantitative acyltransferease studies into cellular growth and function measurements allows a new appraisal of the role of lipids in modifying the function of cellular membrane-associated systems. Comparison of different acyl chains that give different degrees of impairment of growth will be designed to describe the structural features of fatty acids that may influence the induction of new enzymes and initiation of cellular division or mitochondrial replication. The studies are designed to indicate threshold limits on the composition of lipid nutrients that are compatible with normal cell devision and response to inner physiologic regulators. Major differences observed in handling of different positional and geometric isomers of octadecenoic acids raise new questions on the effects that the nutrient acids from partially hydrogenated vegetable oils may have upon cellular functions. The above features, considered as a whole, may well be incorporated into an expanded interpretation of the role dietary lipids in the etiology of heart disease or in the transient necrosis observed after ingesting rapeseed oil.